1. Field of the Invention
The present invention relates to a light emitting display device for use in an LED (light emitting diode) display panel, and in particular, to an inexpensive bright light emitting display device.
2. Description of the Prior Art
Conventionally, as driving methods of a light emitting display device, two types of a static drive type and a dynamic drive type have been put into practical use.
FIG. 33 is a block diagram of a static drive type light emitting display device, while FIG. 35 is a circuit diagram of a static drive type LED dot matrix section.
As shown in FIG. 33, the static drive type light emitting display device has a shift register 216, a latch circuit 217, a driver section 218, and an LED dot matrix section 219. Each LED of the LED dot matrix section 219 is connected to each driver of the driver section 218 one by one.
In the static drive type light emitting display device, serial image signals are successively transmitted to the shift register 216. When the shift register 216 takes in image signals of one screen, the image signals are transmitted from the shift register 216 to the latch circuit 217. The latch circuit 217 drives the driver section 218, with which the driver section 218 lights the LED dot matrix section 219.
The static drive type light emitting display device can continue to light for one screen from a time when the device starts to light the screen to a time when the device takes in a signal of the next screen and starts to display the next screen.
FIG. 34 is a block diagram of a dynamic drive type light emitting display device, while FIG. 36 is a circuit diagram of a dynamic drive type LED dot matrix section.
As shown in FIG. 34, the dynamic drive type light emitting display device comprises a shift register 316, a latch circuit 317, a decoder 320, a driver section 318, and an LED dot matrix section 319.
In the dynamic drive type light emitting display device, serial image signals are successively transmitted to the shift register 316. When the shift register 316 takes in signals of one line, the signals of the one line are transmitted from the shift register 316 to the latch circuit 317. Then, the latch circuit 317 outputs the signals of the one line to the driver section 318 to drive the driver section 318. In the above-mentioned time, an address signal synchronized with the image signal is inputted to the decoder 320. Then, the decoder 320 drives a driver in a driver section 321 for a line corresponding to the image signals, and the driver lights an LED dot matrix section 322. The LED dot matrix section 322 continues to light to a time when the shift register 316 completely takes in signals of the next line and then the driver sections 318 and 321 light the LED dot matrix section 322 with the signals of the next line. In other words, the dynamic drive type light emitting display device performs a dynamic lighting of time-sharingly lighting the LEDs every line. Normally, the dynamic drive type light emitting display device lights the LEDs at a duty ratio of 1/16 or a duty ratio of 1/8.
The static drive type light emitting display device can light the LEDs during an interval of displaying one screen, and therefore the device can provide a bright screen display. However, the static drive type light emitting display device requires drivers corresponding in number to the number of dots of the LEDs had by the LED dot matrix section 322, and further requires a one-to-one connection between each LED and each driver. Furthermore, in order to effect a multi-color light emitting display, the numbers of wiring lines and drivers are required to be doubled or trebled. Therefore, the above-mentioned arrangement results in a complicated wiring for the connection between the LEDs and the drivers together with an increased cost.
On the other hand, in the dynamic drive type light emitting display device, signals are transmitted every scanning line, and therefore the drivers and wiring lines can be reduced in number as compared with the static drive type. However, since one screen is displayed by time-sharingly lighting the LEDs, an average luminance of one LED dot is disadvantageously reduced by some degree attributed to the time-sharing lighting.
Although the drivers and the wiring lines are remarkably reduced in number as compared with the static drive type, for the reason that data signal lines and scanning signal lines are connected to the anodes and the cathodes of the LEDs in an intersecting manner, it is required to wire the signal lines by means of a substrate having a multi-layer structure, disadvantageously resulting in a complicated wiring structure. Furthermore, in order to effect the multi-color light emitting, the wiring lines and the drivers increase in number as compared with a case of a single-color light emitting, resulting in a further complicated wiring structure.